A Low-Cost L-Band Line Amplifier (Rev. 1)

A Low-Cost L-Band Line Amplifier (Rev. 1)
A Low-Cost L-Band Line Amplifier (Rev. 1)
Steven W. Ellingson∗
October 9, 2002
This report documents the design of a low-cost L-band line amplifier. The description presented here is complete, although the design is a minor revision to a
design previous reported in [1]. The change is a reduction in size and a modification
to the enclosure to reduce cost. The cost of the new design is about $44 each in small
quantities.
Although this unit is intended to be used in conjunction with the LNA described
in [2], it may also be useful in other applications. Specifically, this unit provides a
9 VDC bias through the RF input jack which can be used to power the LNA described
in [2]. The intended configuration is for the line amplifier to be located within a few
feet of the LNA, and used to drive a long section (e.g., 100 ft.) of coaxial cable. The
completed line amplifier is shown in Figure 1 and its specifications are summarized
in Figures 2, 3, and 4.
Figure 5 shows a schematic of the line amplifier, with a parts list given in Figure 6.
Components L1 and C1 form a bias-tee, setting the DC voltage at the input jack to
9 VDC, thereby powering the connected LNA. This part of the circuit also forms a
high-pass filter with cutoff at about 200 MHz, which contibutes to the suppression of
strong VHF-band interference, such as FM broadcast radio. MMIC amplifiers U1 and
U2 provide gain and also serve to buffer the stripline bandpass filter, FL1. Figure 7
shows the assembled circuit on its printed circuit board (PCB).
FL1 is a 3-finger interdigital bandpass filter which was designed through a process
of trial-and-error using the “Sonnet” electromagnetic modeling software by Sonnet
∗
The Ohio State University, ElectroScience Laboratory, 1320 Kinnear Road, Columbus, OH
43210, USA. Email: ellingson.1@osu.edu.
1
Figure 1: The line amplifier, as tested.
2
Peak Gain
3 dB Passband
Dimensions
Connectors
Power
18 dB @ 1500 MHz
1250 MHz to 1750 MHz
83 mm × 51 mm × 28 mm
SMA female
100 mA @ 12 VDC
(12–15 VDC accepted)
Figure 2: Specifications
40
30
gain (dB)
20
10
0
−10
−20
−30
0
200
400
600
800
1000
1200
frequency (MHz)
1400
1600
1800
Figure 3: Measured frequency response of line amplifier.
3
2000
40
30
gain (dB)
20
10
0
−10
−20
−30
0
200
400
600
800
1000
1200
frequency (MHz)
1400
1600
1800
2000
Figure 4: Measured frequency response of LNA described in [2] plus the line amplifier
described in this report.
4
12-15
VDC
+9V
VR1
C6
C7
R1
R2
C3
RF IN
9VDC OUT
L3
L2
L1
C5
C4
U1
U2
RF OUT
F1
C1
C9
C11
C2
Figure 5: Schematic.
Value
360
51
39
220
10
0.1
10
10
Unit
Ω
Ω
nH
nH
pF
µF
µF
µF
9
V
Description
Res, 1W, 5%, 2512
Res, 1W, 5%, 2512
Ind, 0805, 5%
Ind, 1210 (3225)
Cap, 1206, 50V
Cap, 0805, X7R
Cap, tant, 35V
Cap, tant, 16V
MMIC Amp
MMIC Amp
Volt. Reg., 7809
Bandpass Filter
PCB
Connector, SMA(F)
4-40 screws
4-40 nuts
Aluminum tube
Aluminum plate
Qty
1
1
1
2
4
3
1
1
1
1
1
1
1
2
4
4
1
1
ID
R1
R2
L1
L2,L3
C1,C2,C9,C11
C3,C4,C5
C6
C7
U1
U2
VR1
FL1
Distributor
Digikey
Digikey
Digikey
Digikey
Digikey
Digikey
Digikey
Digikey
Mini-Circuits
Mini-Circuits
Digikey
ExpressPCB
Digikey
Digikey
Digikey
Figure 6: Parts List.
5
Part Number
P360XCT-ND
P51XCT-ND
PCD1167CT-ND
PCD1123CT-ND
PCC100CCT-ND
PCC1812CT-ND
PCS6106CT-ND
PCS3106CT-ND
RAM-6
ERA-6SM
p/o PCB
rfbch3.pcb
ARFX1232-ND
H150-ND
H216-ND
Unit Cost (Qty)
$0.88 (10)
$0.76 (10)
$0.58 (10)
$0.11 (10)
$1.58 (10)
$0.62 (10)
$4.95 (30)
$3.90 (30)
$0.48 (25)
(p/o PCB)
$62.00 (3)
$4.40 (1)
$0.02 (100)
$0.01 (100)
Figure 7: Circuit assembled on PCB.
Software, Inc. The selected design was as shown in Figure 8. The predicted response
of the filter is shown in Figure 9.
The enclosure consists of the PCB itself (Figures 10 and 11) with an aluminum
spacer and plate to enclose the opposite side. The PCB was obtained from ExpressPCB∗ . The PCB was designed using ExpressPCB’s proprietary PCB layout
software. The PCB layout is shown in Figures 10 and 11. The dimensions of the
dimensions of the PCB are 3-in by 2-in, which allows ExpressPCB’s low-cost “MiniBoard” service to be used. The laminate is 0.062-in FR-4 epoxy glass with a dielectric
constant specified to be between 4.2 and 5.0. The unit is held together with 4-40
screws and nuts.
Acknowledgments
The author is grateful for the assistance of Keith Hampson and Grant Hampson in
creating the enclosure described in this memo.
∗
http://www.expresspcb.com
6
Figure 8: Sonnet model of FL1 used for performance prediction. Shading indicates
metalization. The outer box is assumed to be a perfectly-conducting ground. The
spacing between grid points is 0.045 in. The substrate is assumed to be 0.062-in
thick FR-4 with ²r = 4.6. The substrate is sandwiched between a ground plane and
a layer of air (²r = 1), 1-in thick. Above the air is a continuation of the ground
plane, such that the entire filter (except for the input and output ports) is enclosed
in perfectly-conducting box.
7
Figure 9: Frequency response of FL1 predicted by Sonnet.
8
Figure 10: PCB “top” side (screen dump from layout software).
Figure 11: PCB “bottom” side (screen dump from layout software).
9
References
[1] S.W. Ellingson, “A Low-Cost L-Band Line Amplifier,” Design Report, September
9, 2002.
[2] S.W. Ellingson, “A 1-GHz Highpass PHEMT Low-Noise Amplifier”, Design Report, July 26, 2002.
10
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